The present invention generally relates to the production of a fire-resistant cellulose insulation product, and more particularly to the manufacture of fire-resistant cellulose insulation materials using a process which exclusively involves liquid fire retardant compositions.
Cellulose compositions combined with fire retardant materials are widely used in the construction industry. Specifically, fire-resistant cellulose materials are traditionally used for thermal insulation in the walls and attic spaces of homes and commercial buildings. Insulation products of this type are designed to prevent heat loss and correspondingly insulate building structures from the outside environment. Raw materials used to produce cellulose insulation products may involve many different paper compositions ranging from recycled newspaper to cardboard, paperboard, and fiberboard. These materials are physically processed to produce a finely-divided material having a low bulk density.
To achieve an approved level of flame and/or smolder resistance, the selected cellulose materials are combined with fire retardant compositions during the production process. Many different fire retardants may be used for this purpose, which are traditionally applied in powder form. Exemplary fire retardant compositions include but are not limited to monoammonium phosphate, diammonium phosphate, boric acid, aluminum sulfate, ammonium sulfate, sodium tetraborate and mixtures thereof. These materials, as well as other fire retardant compositions and additional information regarding the production of cellulose insulation products are discussed in U.S. Pat. Nos. 4,168,175 to Shutt and 4,595,414 to Shutt which are incorporated herein by reference.
After combining the selected fire retardant compositions and cellulose materials, the resulting product is physically processed using conventional mechanical devices (e.g. hammermill systems known in the art) to produce a pulverized, finely divided insulation product. In accordance with traditional processing technology, fire-resistant cellulose insulation products are specifically prepared using one of two basic methods. In a first method, the selected cellulose materials (e.g. recycled/used paper products) are subjected to multi-stage size reduction by grinding or other conventional processes using standard equipment including but not limited to hammermill systems. At selected stages during the size reduction process, a fire retardant composition in powder (dry) form is combined/mixed with the cellulose materials. In a preferred embodiment, mixing of these ingredients is undertaken at or near the final grinding/shredding stages of the system.
Alternative "hybrid-type" systems have been developed which involve addition of fire retardant compositions in powder (dry) form at or near the final size-reduction stages of the system in combination with the use of a liquid fire retardant composition in the initial stages of production. However, both of these systems require the use of powdered (dry) fire retardant compositions which present numerous disadvantages. These disadvantages include but are not limited to (1) the generation of substantial amounts of dust which requires elaborate safety and environmental control systems; (2) an increased amount of processing machinery which is needed to handle and deliver powdered chemical compositions; (3) the need to use large amounts of chemicals (e.g. fire retardants) due to production inefficiencies associated with powder-type systems; and (4) increased material costs associated with the need to use large quantities of powdered chemicals.
The present invention involves a unique and distinctive all-liquid fire retardant system which entirely avoids the use of any fire retardants in powdered (dry) form. As described below, the claimed system includes a unique combination of process steps which efficiently produce a cellulose insulation product in a highly effective manner while avoiding the problems listed above. Furthermore, the claimed process provides numerous important and substantial advantages not attainable by powder-based systems including but not limited to (1) the substantial elimination of dust problems and the safety considerations/control equipment associated therewith; (2) a reduction in the amount and complexity of processing equipment needed to manufacture the insulation product; (3) a substantial reduction in chemical (e.g. fire retardant) use; and (4) a corresponding reduction in material costs due to decreased chemical use.
In addition to the benefits provided above, the final insulation product manufactured in accordance with the invention readily meets all applicable government requirements and has a lower average bulk density compared with materials produced using powdered fire retardants. The term "bulk density" as used herein shall be defined to encompass the weight (traditionally in lbs./ft.sup.3) of the final installed/settled insulation product. A final product with a low bulk density is desired because it imparts less weight to the building structure in which it is used. In addition, it is more free-flowing, easier to handle, and more readily installed. Furthermore, the fiber materials in the completed product have a higher degree of rigidity which results in less settling of the product when used in a building structure compared with conventionally-prepared insulation products. Minimal settling of the insulation product is beneficial because it enables less of the product to be used, thereby providing significant cost savings. Finally, the completed insulation product is characterized by a substantial absence of detached fibrous residue which, if present, can reduce the fire/heat resistance of the final insulation product and increase its density. Accordingly, the present invention represents an advance in the art of cellulose insulation manufacture, and provides many economic, safety, quality-control, and other benefits compared with powder-based systems as discussed below.